Modern vehicles are equipped with exhaust gas treatment devices, known as catalytic converters, that convert toxic gases such as hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) into substances such as carbon dioxide (CO2), nitrogen (N2) and water (H2O). A known problem with catalytic converters is that certain substances can remain, for example by physical or chemical adsorption, on internal surfaces of the converters, and reduce the capacity of the converters. Such detrimental adsorption is known as catalytic converter poisoning. For example, fuels, whether gasoline or diesel, for vehicle internal combustion engines, contain a relatively high amount of sulfur, typically depending on in which state or region they are provided. The sulfur creates problems for the operation of the catalyst exhaust gas treatment devices. In the engine combustion process, the sulfur is converted to sulfur oxides (SOx), which adsorbs strongly to internal surfaces of the catalyst and therefore reduces its exhaust gas treatment capacity. This process is often referred to as sulfur poisoning. Sulfur adsorption is particularly strong during low load driving conditions.
A number of catalytic converter regeneration measures to solve this problem have been suggested. It is well known that the catalytic converter can be restored from sulfur poisoning (i.e., subjected to sulfur regeneration) by being exposed to high temperatures.
It is also known, for example through US2003/0224907A1 or EP0931923A1, to allow fuel into non-combusting cylinders, to be combusted with air in a catalytic converter in the exhaust system. Such combustion in the catalytic converter can be used to heat it for sulfur regeneration. A problem encountered at such sulfur regeneration is that high temperatures can occur at the upstream end of the catalytic converter, threatening to damage it. Also, at downstream portions of the catalytic converter, the temperature might not be high enough during regeneration to provide effective restoration from sulfur poisoning.